JP6285397B2 - Ag paste and Ag powder for Ag paste - Google Patents

Description

  The present invention relates to an Ag paste. Specifically, the present invention relates to an Ag paste capable of forming an electrode (particularly a fine line electrode) excellent in conductivity by low-temperature firing for a short time.

  In recent years, attempts have been made to form electronic wiring on a low heat-resistant member made of polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or the like from the viewpoints of weight reduction, cost reduction, and easy processability. Such electronic wiring is made of, for example, PEN or PET constituting the low heat resistant member by applying an Ag paste containing Ag powder (including slurry and ink; the same shall apply hereinafter) to the surface of the low heat resistant member. It is manufactured by firing at a temperature lower than the heat-resistant temperature (a temperature at which problems such as distortion of the member hardly occur, for example, 150 ° C. or less).

  Patent Literatures 1 to 4 disclose an Ag powder that can be used for such applications and an Ag paste containing the Ag powder. For example, Patent Document 1 discloses a coated silver ultrafine particle covered with a protective molecular amine (protective agent) having a particle size of 30 nm or less, and an Ag paste containing the coated silver ultrafine particle. In Patent Document 1, the particle size of Ag fine particles is reduced to 30 nm or less so that the melting temperature is lowered and sintering at a low temperature is possible. Moreover, the stability as fine particles is maintained by coating the surface of the Ag fine particles with a protective agent.

JP 2010-265543 A JP 2013-142173 A JP 2014-031542 A JP 2014-194057 A

However, according to the study by the present inventors, there is still room for improvement when the above prior art is applied to, for example, the formation of fine line electrodes (thin wire electrodes).
That is, since the coated silver ultrafine particles described in Patent Document 1 are very fine with a particle size of 30 nm or less, they contain a large amount of protective agent from the viewpoint of stabilizing the surface of the fine particles. For this reason, at the time of baking, the said large amount of protective agent burns out and the thermal contraction rate of Ag fine particle itself becomes large. In addition, many pores are generated in the obtained sintered body, which causes a decrease in filling properties. As a result, the fine line electrode using the above-mentioned coated silver ultrafine particles has a problem that it is highly brittle and easily breaks or the conductivity is lowered. In addition, in the above-described prior art, when the firing temperature is extremely low, such as 100 ° C. or less, long-time firing is required to achieve practically excellent conductivity (for example, volume resistivity on the order of μΩ · cm). Necessary. Since the firing time greatly affects the production efficiency, it is desired to shorten the firing time even by 1 second particularly in continuous production such as a roll-to-roll process.

  The present invention has been made in view of these circumstances, and an object thereof is to provide an Ag paste capable of forming an electrode (particularly, a fine line electrode) having excellent conductivity by low-temperature firing for a short time.

The inventors focused on the balance between the sinterability of Ag powder and the surface stability and made extensive studies. As a result, the present invention has been created.
According to the present invention, an Ag paste containing Ag powder and a dispersion medium is provided. The Ag powder has the following conditions: (1) In a number-based particle size distribution, the D ₅₀ particle size corresponding to the cumulative 50% by number from the smallest particle size is 80 nm or more and 200 nm or less; (2) Aspect ratio 1 The ratio of spherical Ag fine particles of less than 5 is 60% by number or more and less than 85% by number of the total Ag fine particles constituting the Ag powder; (3) a protective agent comprising an organic amine having 5 or less carbon atoms on the surface; (4) When the total Ag powder is 100% by mass, the protective agent is 1.2% by mass or less. The dispersion medium is composed of a solvent having a boiling point of 150 ° C. or less at atmospheric pressure.

According to the Ag paste, it is possible to form an electrode having high density and high filling property and excellent conductivity by firing at a low temperature for a short time. For example, the volume resistivity is 10 μΩ · cm or less under firing conditions of 100 ° C./10 minutes, the volume resistivity is 25 μΩ · cm or less under firing conditions of 80 ° C./10 minutes, and the volume resistivity is under firing conditions of 80 ° C./30 minutes. Of 10 μΩ · cm or less can be stably realized. It is preferable from the viewpoint of low cost and environmental load reduction (for example, energy saving and CO ₂ reduction) that baking is completed at a low temperature and in a short time.

In addition, the particle size distribution of the Ag powder contained in the Ag paste can be grasped as follows, for example. That is, first, using a general FE-SEM, the Ag powder is observed at an appropriate magnification (for example, 5 to 100,000 times), and several (for example, four) FE-SEM observation images are obtained for each sample. . Next, 100 or more (for example, 100 to 1000) fine particles that are independent (non-overlapping) in the observed image are arbitrarily extracted, and an image that traces the outline of each fine particle is created. This image is analyzed by the image analysis software “Image Pro” manufactured by Media Cybernetics, and the particle size (equivalent circle diameter) is calculated from the area value of the fine particles. By expressing the result in a graph in which the horizontal axis represents the particle size of the fine particles and the vertical axis represents the number of fine particles, a number-based particle size distribution can be obtained.
The aspect ratio can be calculated as the ratio of the short diameter to the long diameter of the fine particles based on the FE-SEM observation image.

In a preferred embodiment of the Ag paste disclosed herein, in the number-based particle size distribution, the D ₉₀ particle size corresponding to the cumulative 90% by number from the smaller particle size and the cumulative 10% by number from the smaller particle size. and _{D 10} particle size corresponding to the following formula _{(1): 70nm ≦ (D} 90 particle size _{-D 10} particle size); meet. Thereby, it is possible to realize an electrode that is filled with Ag powder at a high density and is further excellent in conductivity.

In a preferred embodiment of the Ag paste disclosed herein, in the number-based particle size distribution, the D ₉₀ particle size corresponding to the cumulative 90% by number from the smaller particle size and the cumulative 10% by number from the smaller particle size. The D ₁₀ particle size corresponding to the above and the D ₅₀ particle size are expressed by the following formula (2): 0.6 ≦ [(D ₉₀ particle size−D ₁₀ particle size) / D ₅₀ particle size] ≦ 1.2. Is satisfied. As a result, a dense and highly filled electrode can be realized. Therefore, problems such as electrode cracks can be highly prevented.

In one preferred embodiment of the Ag paste disclosed herein is the _{D 10} particle size 50nm or more. In another preferred embodiment of the Ag paste disclosed herein, the D ₉₀ particle size is 310 nm or less. By satisfying at least one of the D ₁₀ particle size and the D ₉₀ particle size, it is possible to achieve both low-temperature sintering and surface stability Ag powder at a higher level. Furthermore, a fine wire electrode can be formed more stably by satisfying the above _D90 particle size.

As another aspect of the present invention, an Ag powder for use in the Ag paste is provided. Such Ag powder has the following conditions: (1) In a number-based particle size distribution, the D ₅₀ particle size corresponding to the cumulative 50% by number from the smallest particle size is 80 nm or more and 200 nm or less; (2) Aspect ratio 1 The ratio of spherical Ag fine particles of less than 5 is 60% by number or more and less than 85% by number of the total Ag fine particles constituting the Ag powder; (3) a protective agent comprising an organic amine having 5 or less carbon atoms on the surface; (4) When the total Ag powder is 100% by mass, the protective agent is 1.2% by mass or less.

It is a FE-SEM observation image of Ag powder (ae, gj). It is a graph which shows the particle size distribution of the number reference | standard of Ag powder (ae). It is a graph which shows the particle size distribution of the number basis of Ag powder (gj). It is a graph which shows distribution of the aspect ratio of the number basis of Ag powder (ae). It is a graph which shows distribution of the aspect ratio of the number basis of Ag powder (gj). 2 is a photograph of sintered bodies according to Example 1 and Reference Example 1. It is a FE-SEM observation image of the sintered compact after baking Ag powder for 10 minutes at 100 degreeC, Comprising: (a) is an image which concerns on Example 1, (b) is an image which concerns on the reference example 1. FIG. It is explanatory drawing of the discharge test using a dispenser.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than those specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, constituents other than Ag powder and dispersion medium, general techniques relating to the preparation of Ag paste, etc.) ) Can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

[Ag paste]
The Ag paste disclosed here contains (A) Ag powder and (B) a dispersion medium as essential components. In addition, other components can be blended in light of various standards.
Hereinafter, the constituent components of the Ag paste disclosed herein will be described.

≪ (A) Ag powder≫
The Ag powder is an aggregate of silver (Ag) fine particles and has the following characteristics (1) to (4):
(1) Particle Size _{Distribution: D 50} particle size is 80nm or more 200nm or less;
(2) The ratio of spherical Ag fine particles having an aspect ratio of less than 1.5 is 60% by number or more and less than 85% by number of the whole Ag fine particles constituting the Ag powder;
(3) Protective agent: A protective agent comprising an organic amine having 5 or less carbon atoms is attached to the surface;
(4) Proportion of protective agent: The proportion of protective agent is 1.2% by mass or less;
By having the above, it has both excellent low temperature sinterability and surface stability. In other words, the Ag powder disclosed herein is characterized by the fact that the fine particles themselves have high stability while maintaining low-temperature sinterability. Hereinafter, each feature will be described in order.

(1) Particle size distribution The Ag powder of the Ag paste disclosed herein is of a size suitable for low-temperature (at 150 ° C. or lower) sintering, and the stability of the fine particles themselves is enhanced. And That is, in general, it can be said that fine particles having a small particle size are suitable for sintering at a low temperature, but if the particle size is too small, surface stability is insufficient and a large amount of protective agent is required. On the contrary, it can be said that the larger the particle size, the higher the surface stability. However, if the particle size is too large, the melting temperature becomes high and sintering at a low temperature becomes difficult. For this reason, it is important to balance low-temperature sinterability and surface stability.

Specifically, Ag powder of Ag paste disclosed herein is in the particle size distribution of the _{number-based, D 50} particle size (average particle diameter) of 80nm or more 200nm or less. When the D ₅₀ particle size is 80 nm or more (typically 90 nm or more), for example, the surface of the fine particles is stabilized with a smaller protective agent content than when the D ₅₀ particle size is very small, for example, less than 30 nm. It becomes possible to do. Further, when the D ₅₀ particle size is 200 nm or less (typically 190 nm or less), the melting temperature is kept low, and sintering at a low temperature such as 150 ° C. or less becomes possible.

In a preferred embodiment, in the number-based particle size distribution, the minimum particle size ( _Dmin particle size) is 10 nm or more, preferably 20 nm or more, for example 30 nm or more. In other words, it is preferable to contain substantially no ultrafine particles of less than 10 nm, preferably less than 20 nm, for example less than 30 nm.
In another preferred aspect, the particle size distribution of the number-based, person D ₅ particle size 40nm or more, which corresponds to the cumulative 5% by number from the small particle size, typically not less than 45 nm, for example, 90nm or less It is.
In another preferred embodiment, in the number-based particle size distribution, the D ₁₀ particle size corresponding to a cumulative number of 10% from the smallest particle size is 45 nm or more, typically 50 nm or more, for example, 100 nm or less. It is.
In another preferred embodiment, in the number-based particle size distribution, the D ₂₀ particle size corresponding to the cumulative 20% by number from the smaller particle size is 60 nm or more, typically 65 nm or more, for example, 130 nm or less. It is.

By setting at least one of the D _min particle size, D ₅ particle size, D ₁₀ particle size, and D ₂₀ particle size to a predetermined value or more, the ratio of ultrafine particles having low surface stability is reduced, and Ag powder Overall stability and storage stability can be improved. Preferably, the content of the protective agent can be further reduced. Furthermore, the handleability and workability of Ag powder can be improved.
Further, by setting at least one of the D _min particle size, the D ₅ particle size, the D ₁₀ particle size, and the D ₂₀ particle size to a predetermined value or less, the low temperature sinterability can be improved.

In another preferred embodiment, in the number-based particle size distribution, the maximum value of particle size (D _max particle size) is 600 nm or less, preferably 550 nm or less, for example, 520 nm or less. In other words, it is preferable that substantially no coarse particles of more than 600 nm, preferably more than 550 nm, for example more than 520 nm are contained.
In another preferred embodiment, in the particle size distribution based on the number, the D ₈₀ particle size corresponding to the cumulative 80% by number from the smaller particle size is 100 nm or more, typically 110 nm or more, Is 270 nm or less, for example 260 nm or less.
In another preferred embodiment, in the particle size distribution based on the number, the D ₉₀ particle size corresponding to the cumulative 90% by number from the smaller particle size is 110 nm or more, for example 120 nm or more, and 320 nm or less, typically Is 310 nm or less, for example, 305 nm or less.
In another preferred embodiment, in the particle size distribution based on the number, the D ₉₅ particle size corresponding to the cumulative 95% by number from the smaller particle size is 130 nm or more, for example, 140 nm or more, and typically 400 nm or less. For example, it is 350 nm or less.

By setting at least one of the D _max particle size, the D ₈₀ particle size, the D ₉₀ particle size, and the D ₉₅ particle size to a predetermined value or more, the surface stability of the Ag powder can be maintained at a high level.
Further, by setting at least one of the D _max particle size, D ₈₀ particle size, D ₉₀ particle size, and D ₉₅ particle size to a predetermined value or less, the sintering temperature of the Ag powder can be further lowered. . Furthermore, precise formation of a fine line electrode having a narrow line width can be suitably realized.

The Ag powder of the Ag paste disclosed herein preferably has an appropriate spread in the particle size distribution. _{Specifically,} a value obtained by subtracting the _{D 10} particle size from the _{D 90} particle size _{(D 90} particle size _{-D 10} particle size) is 70nm or more, typically be more than 75 nm, generally 220nm or less, for example 210nm or less It is good to be. By setting the value of (D ₉₀ -D ₁₀ ) to a predetermined value or more, the Ag fine particles having a relatively small particle size fill a gap between the Ag fine particles having a relatively large particle size when the Ag powder is sintered. Can be sintered. As a result, Ag powder is packed (packed) with higher density, and more excellent conductivity can be realized.

In one preferred _embodiment, the value obtained by subtracting the _{D 5} particle size from _{D 95} particle size _{(D 95} particle size -D ₅ particle size) is more than 90 nm, typically be more than 95 nm, generally 270nm or less, for example 260nm It is as follows.
In another preferred _aspect, a value obtained by subtracting the _{D 20} particle size from the _{D 80} particle size _{(D 80} particle size _{-D 20} particle size) is 40nm or more, typically not less than 45 nm, generally 150nm or less, For example, it is 140 nm or less.
In another preferred embodiment, a value obtained by subtracting the D _min particle size from the D _max particle size (D _max particle size−D _min particle size) is 150 nm or more and approximately 500 nm or less.
The _{(D 95} -D 5), by satisfying at least one of _{(D 80} particle size _{-D 20} particle size) and _{(D max} particle size _{-D min} particle size), it is possible to improve the filling property . Moreover, low temperature sinterability and surface stability can be balanced at a higher level.

In another preferred embodiment, the spread of the particle size distribution calculated from the D ₅₀ particle size, the D ₉₀ particle size, and the D ₁₀ particle size W: W = (D ₉₀ particle size−D ₁₀ particle size) / D ₅₀ particles The diameter is typically 0.6 or more, preferably 0.7 or more. Incidentally, W is not less than the predetermined value is a particle size distribution broad, which indicates that it has a predetermined extent from the D ₅₀ particle size. As a result, a dense and highly fillable electrode can be realized, and defects such as electrode cracking can be highly prevented.
The spread W of the particle size distribution is typically 1.2 or less, preferably 1.1 or less. Note that W is less than the predetermined value, it indicates that the only excessively broad particle size distribution, maintains a predetermined homogeneity converging to some extent in the range of D ₅₀ particle size. Thereby, an electrode having high homogeneity and filling properties and excellent conductivity can be stably realized.

Furthermore, in one preferred embodiment, _{D 5} particle size of the value obtained by dividing the ₉₅ grain diameter _{D (D 5} particle size _{/ D 95} particle size) is generally 0.2 or more, there is for example 0.24 or more, preferably 0.5 or less, typically 0.4 or less.
In another preferred _aspect, a value obtained by dividing the _{D 10} particle size in the _{D 90} particle size _{(D 10} particle size _{/ D 90} particle size) is generally 0.3 or more, there is for example 0.33 or more, preferably 0.6 or less, typically 0.55 or less.
The above _{(D 5} particle size _{/ D 95} particle size) and _{(D 10} particle size _{/ D 90} particle size) takes a value in the range of 0 to 1, the particle size of the Ag fine particles constituting the Ag powder all When equal, it becomes 1, and as the particle size distribution becomes wider, it becomes closer to 0. When at least one of the two ratios satisfies the above range, one or more of the balance between low temperature sinterability and surface stability, fillability, and conductivity can be improved.

In another preferred embodiment, the number-based particle size distribution in which the horizontal axis represents the particle size of the fine particles and the vertical axis represents the number of fine particles is unimodal. In this case, the particle size distribution of the peak top (maximum point) is typically slightly greater range than roughly equivalent to the D ₅₀ particle size it may in particular in 210nm following range of 90 nm. That is, it is the particle size distribution is in a normal distribution like that a substantially median D ₅₀ particle size. Thereby, it is possible to suitably realize a dense electrode having high filling properties and excellent conductivity.

(2) Aspect ratio The shape of the Ag fine particles constituting the Ag powder of the Ag paste disclosed herein may be, for example, spherical, elliptical, crushed, scale-like, plate-like, or fiber-like. One index representing the particle shape is the aspect ratio. The aspect ratio is calculated as the ratio of the length of the minor axis to the length of the major axis (major axis / minor axis) for each Ag fine particle constituting the Ag powder. Here, the arithmetic average value of the aspect ratio for each Ag fine particle is adopted as the aspect ratio of the Ag powder. Note that the aspect ratio is closer to 1, the more isotropic, that is, the three-dimensional shape of the Ag fine particles becomes closer to a sphere. On the other hand, the larger the aspect ratio, the higher the anisotropy, that is, the three-dimensional shape of the Ag fine particles becomes non-spherical, for example, a flat shape such as a plate shape or a fiber shape. Here, Ag fine particles having an aspect ratio of less than 1.5 are referred to as “spherical particles”, and Ag fine particles having an aspect ratio of 1.5 or more are referred to as “non-spherical particles”.

In the Ag fine particles constituting the Ag powder disclosed herein, the proportion of spherical Ag fine particles having an aspect ratio of less than 1.5 is 60% by number or more of the total Ag powder. In other words, non-spherical Ag fine particles having an aspect ratio of 1.5 or more are less than 40% by number of Ag fine particles constituting the Ag powder. With such a particle shape, dispersibility and storage stability in the Ag paste, and / or surface smoothness, homogeneity, and filling property in the sintered body are effectively enhanced. As a result, a dense electrode having high toughness and excellent conductivity can be suitably realized.
In a more preferred embodiment, 70% or more, for example 75% or more, of the total Ag powder is spherical Ag fine particles having an aspect ratio of less than 1.5. Thereby, the above-mentioned effect can be exhibited at a higher level.

  In the Ag fine particles constituting the Ag powder disclosed herein, the proportion of spherical Ag fine particles having an aspect ratio of less than 1.5 is less than 85% by number, for example, 83% by number or less of the total Ag powder. In other words, the non-spherical Ag fine particles having an aspect ratio of 1.5 or more are 15% by number or more, for example, more than 17% by number among Ag fine particles constituting the Ag powder. That is, the Ag powder disclosed here is a mixture of spherical Ag fine particles (spherical particles) and non-spherical Ag fine particles (non-spherical particles). In such an Ag powder, for example, a spherical body enters a gap in which non-spherical particles are arranged, so that a sintered body having a high packing property can be obtained. Therefore, the contact area between the Ag fine particles is increased, and an electrode having further excellent conductivity can be realized. In one example, non-spherical particles have a relatively large particle size compared to spherical particles. Thereby, an electrode with higher surface smoothness can be realized.

In another preferred embodiment, 90% by number or more, for example, 95% by number or more, and generally 98% by number or less of the total Ag powder has an aspect ratio of less than 2.0. In other words, the ratio of the Ag fine particles having an aspect ratio of 2.0 or more is preferably 2% by number or more of the Ag fine particles constituting the Ag powder. Thereby, the above-mentioned effect can be exhibited at a higher level.
In another preferred aspect, the maximum aspect ratio is 3 or more, for example, 3.5 or more. In other words, the Ag powder contains Ag fine particles with remarkably high anisotropy. The maximum aspect ratio is, for example, 10 or less, typically 9 or less. Thereby, even a fine line electrode having a narrow line width can be formed uniformly (evenly).

(3) Protective agent The Ag powder of the Ag paste disclosed herein includes a protective agent on the surface thereof. Typically, the surface of the Ag powder is coated with a protective agent. Thereby, the surface stability of Ag microparticles | fine-particles can be maintained and aggregation of Ag microparticles | fine-particles can be suppressed efficiently. As a result, a uniform (non-uniform) coating film can be formed. Furthermore, an Ag paste having excellent long-term storage stability can be realized.
As the protective agent, those that are more easily detached are preferable from the viewpoint of realizing low-temperature firing for a short time. For example, those having a low boiling point at atmospheric pressure and capable of forming a relatively weak bond (for example, coordination bond) with silver are preferable. This organic amine may contain, for example, an alkoxy group such as a methoxy group or an ethoxy group in the structure.

  Therefore, in the technique disclosed herein, an organic amine having 5 or less carbon atoms is used as a protective agent. Specific examples of the organic amine having 5 or less carbon atoms include methylamine, ethylamine, n-propylamine, isopropylamine, butylamine, pentylamine, 2-methoxyethylamine, 2-ethoxyethylamine, 3-methoxypropylamine, and 3-ethoxy. Primary aliphatic amines such as propylamine; Secondary aliphatic amines such as dimethylamine, diethylamine, methylbutylamine, ethylpropylamine, and ethylisopropylamine; Tertiary aliphatics such as trimethylamine, dimethylethylamine, and diethylmethylamine An amine; These organic amines can be used individually by 1 type or in mixture of 2 or more types.

In a preferred embodiment, the organic amine has 3 or more carbon atoms, typically 4 or more. According to this aspect, the stability of the surface of the fine particles can be more effectively enhanced while maintaining low temperature sinterability.
In another preferred embodiment, the protective agent has a boiling point at atmospheric pressure of 150 ° C. or lower, for example, 70 to 150 ° C. Thereby, the effect mentioned above can be exhibited at a higher level.

(4) Proportion of protective agent In order to exhibit high conductivity by low-temperature firing for a short time, it is important to reduce the proportion of the protective agent as much as possible and keep the thermal shrinkage rate of the Ag fine particles after firing small. . In the technique disclosed here, the content ratio of the protective agent is significantly lower than the conventional one by setting the particle diameter of the Ag fine particles in the above range. Specifically, when the entire Ag powder is 100% by mass, the proportion of the protective agent is 1.2% by mass or less. In other words, silver accounts for 98.8% by mass or more of the entire Ag powder. From the viewpoint of keeping the thermal shrinkage rate small, the ratio of the protective agent is lower, preferably 1.1% by mass or less, for example 1% by mass or less. Thereby, lowering of the firing temperature and / or shortening of the firing time can be realized at a higher level. Furthermore, an electrode having high density and excellent electrical conductivity can be realized even by low-temperature firing for a short time.

  In a preferred embodiment of the Ag powder disclosed herein, a component that can generate a corrosive gas during the sintering of the Ag powder (a corrosion-causing component) is substantially not included. That is, for example, it is permissible for corrosion-causing components to be inevitably mixed due to the Ag powder manufacturing process or manufacturing equipment, but at least actively, these components are not added. Specific examples of corrosion-causing components include halogen components such as fluorine (F) and chlorine (Cl), sulfur (S) components, and the like. By substantially not including corrosion-causing components, it is possible to highly suppress corrosion deterioration of the firing equipment and alteration of the substrate for electrode formation. Of course, it is also preferable not to include components that may adversely affect the human body and the environment, such as lead (Pb) components and arsenic (As) components.

  The proportion of the (A) Ag powder in the entire Ag paste may be adjusted according to, for example, the thickness of the electrode to be formed, and is not particularly limited. As an example, the ratio of the Ag powder is preferably approximately 60% by mass or more, for example 70% by mass or more, and 85% by mass or less, for example 80% by mass or less, based on the entire Ag paste. Thus, by increasing the proportion of the Ag powder, the denseness of the electrode can be further improved. As a result, it is possible to stably realize an electrode that is more excellent in conductivity by short-time firing. Further, even when a relatively thick electrode (for example, a thickness of 10 μm or more) is formed, the Ag paste is less sagging and can be stably formed with a uniform thickness.

≪Manufacture of Ag powder≫
Such an Ag powder may be produced according to a conventionally known method, and the production method is not particularly limited. In other words, properties of the Ag powder is above (1) ~ (4) ( D 50 particle size, aspect ratio, and the type and amount of protective agent) if noted to meet, can be produced by any method. In one preferred embodiment, the method may be produced by a method including the following steps: (i) preparation of a mixed solution; (ii) reduction of silver (Ag) salt in the mixed solution; (iii) washing of Ag fine particles. it can.

(I) First, an organic amine as a protective agent and a particle size controlling agent are mixed at room temperature (for example, 25 ± 5 ° C.) to prepare a solution. The organic amine may have 5 or less carbon atoms, and for example, the above-described compounds can be used. The particle size control agent is an additive for controlling the particle size of Ag fine particles by adjusting the reaction rate of Ag ions and the coordination amount of organic amine to Ag. Specifically, for example, coordination compounds such as alcohols and amides can be considered. For example, when the solubility of the organic amine in the particle size controlling agent is low, a solvent may be used as appropriate.
Next, typically at room temperature, a silver salt as an Ag source is added to the above mixed solution and mixed with stirring. It does not specifically limit as silver salt, For example, organic acid silver salts, such as silver oxalate, silver acetate, silver formate, can be used. Among these, silver oxalate is preferable because it can easily generate metallic silver by heating in the subsequent reduction step and does not generate a by-product.

(Ii) Next, the silver salt is reduced to deposit metallic silver. Reduction is performed by, for example, thermal decomposition, photoreaction, addition of a reducing agent, or the like. The deposited metallic silver (Ag fine particles) typically may have a surface whose surface is protected with an organic amine.
(Iii) Next, the precipitated Ag fine particles are washed with a solvent. As a solvent used for washing, for example, a solvent used as a dispersion medium for Ag paste can be considered.

  In a preferred embodiment, the Ag fine particles are maintained in a wet state without isolation or drying of the Ag powder after the step (iii). And it is used for preparation of Ag paste, maintaining the said wet state. According to the study by the present inventors, aggregation of Ag fine particles is suppressed thereby, and an Ag paste having high dispersion stability and high homogeneity can be obtained.

Note that Ag powder satisfies the above range aspect ratio, crystal planes selectively influences may give component (e.g. Cl ^-, etc.) when performing the reaction without addition of may. The particle diameter distribution and D ₅₀ particle size of the Ag powders, for example, can be adjusted by the kind and amount of the particle size control agent (e.g., molar ratio of the particle size control agent and an organic amine).

≪ (B) Dispersion medium≫
The dispersion medium is for dispersing the solid content of the Ag paste (that is, the Ag powder). By including a dispersion medium in the Ag paste, workability, applicability, and moldability can be improved, and a uniform coating film can be stably formed.

  The dispersion medium of the Ag paste disclosed herein is not particularly limited except that the boiling point at atmospheric pressure is 150 ° C. or less, and various solvents can be used. Specific examples (and their boiling points) include dichloromethane (methylene chloride, boiling point 40 ° C), trichloromethane (chloroform, boiling point 61 ° C), methyl acetate (boiling point 57 ° C), ethyl acetate (boiling point 77 ° C), 2-propanone (acetone). , Boiling point 57 ° C), 2-butanone (methyl ethyl ketone, boiling point 80 ° C), diethyl ether (boiling point 35 ° C), tetrahydrofuran (boiling point 66 ° C), acetonitrile (boiling point 82 ° C), benzene (boiling point 80 ° C), toluene (boiling point 110) ° C), methanol (boiling point 65 ° C), ethanol (boiling point 78 ° C), 1-propanol (boiling point 98 ° C), 2-propanol (boiling point 82 ° C), 1-butanol (boiling point 117 ° C), 1-pentanol (boiling point) Organic solvent such as 138 ° C.). These solvents can be used alone or in combination of two or more compatible ones.

In a preferred embodiment, the boiling point of the dispersion medium at atmospheric pressure is 140 ° C. or lower, preferably 130 ° C. or lower, such as 120 ° C. Thereby, the firing temperature can be lowered and / or the firing time can be shortened. Therefore, the effect of the present invention can be exhibited at a higher level.
In another preferred embodiment, the boiling point of the dispersion medium at atmospheric pressure is 35 ° C. or higher, preferably 40 ° C. or higher, more preferably 50 ° C. or higher, for example 100 ° C. or higher. Accordingly, it is possible to maintain and ensure appropriate workability and handling properties even in a relatively high room temperature environment such as a summer heat wave.

  The proportion of the (B) dispersion medium in the entire Ag paste is not particularly limited as long as the Ag powder can be uniformly dispersed, and can be adjusted according to, for example, the thickness of the electrode to be formed. As an example, the ratio of the dispersion medium may be approximately 15% by mass or more, for example, 20% by mass or more, and 40% by mass or less, for example, 30% by mass or less of the entire Ag paste. Thereby, for example, even when a thick electrode is formed, it is possible to prevent sagging or bleeding of the Ag paste during application. As a result, it is possible to suppress the expansion of the line width of the electrode and the unevenness of the thickness. Furthermore, the denseness of the electrode can be further increased, and higher conductivity can be realized.

≪ (C) Other ingredients≫
In addition to the Ag powder and the dispersion medium, various additive components can be added to the Ag paste disclosed herein as necessary. That is, the Ag paste may or may not contain (C) other components. Examples of such components include binders, inorganic fillers, surfactants, dispersants, thickeners, antifoaming agents, plasticizers, stabilizers, antioxidants, pigments and the like. As these components, those known to be usable for Ag paste can be appropriately used.
However, it is desirable that the Ag paste does not substantially contain a component (corrosion-causing component) that can generate a corrosive gas during firing. Specific examples of corrosion-causing components include halogen components such as fluorine (F) and chlorine (Cl), sulfur (S) components, and the like. Thereby, the corrosion deterioration of a baking equipment and the quality change of the board | substrate for electrode formation can be suppressed highly. Of course, it is also preferable not to include components that may adversely affect the human body and the environment, such as lead (Pb) components and arsenic (As) components.

The proportion of (C) other components in the entire Ag paste can be arbitrarily set as long as the effects of the present invention are not significantly impaired, and are not particularly limited. As an example, the proportion of other components may be approximately 20% by mass or less, typically 10% by mass or less, for example, 5% by mass or less of the entire Ag paste. Thereby, the electrode excellent in electroconductivity is realizable by baking at low temperature for a short time.
For example, when the binder is included in the Ag paste, the ratio of the binder is approximately 0.1% by mass or more, typically 0.5% by mass or more, for example, 1% by mass or more of the entire Ag paste, It may be about 10% by mass or less, typically 5% by mass or less, for example, 3% by mass or less. Thereby, it is possible to realize an electrode excellent in adhesiveness and integrity with the base material while maintaining excellent conductivity.

In the prior art, for example, a binder is added to the Ag paste from the viewpoint of improving workability at the time of applying the Ag paste, temporarily fixing solid components, or improving the shape retention (durability) of the sintered body. It is common to do. However, if a binder component residue remains in the sintered body even after low-temperature firing for a short time, the conductivity may be hindered and the resistance may be significantly increased.
On the other hand, the Ag paste disclosed here can realize a dense sintered body having high toughness without including a binder. For this reason, the aspect which does not contain a binder in Ag paste (binder free) is possible. In an electrode using a binder-free Ag paste, the filling property is improved, and a denser and higher conductivity can be realized. Moreover, lowering of the firing temperature and shortening of the firing time can be realized more suitably.
In a preferred embodiment, the Ag paste is composed of the Ag powder and a dispersion medium. Thereby, the effect of this invention can be exhibited more stably and at a higher level.

[Preparation of Ag paste]
Such an Ag paste can be prepared by weighing the above-described constituent materials so as to have a predetermined content (mass ratio), and stirring and mixing them uniformly. The materials can be stirred and mixed using various conventionally known stirring and mixing devices.
In one preferred example, the Ag powder is always kept wet from the synthesis (production) of the Ag powder to the preparation of the Ag paste. According to the study by the present inventors, when the Ag powder is dried, problems such as formation of aggregates, solidification and precipitation, and the like may occur. In particular, when the content of Ag powder is high (the content of the dispersion medium is low) and no additive such as a binder is contained in the Ag paste, such a problem is likely to occur. For this reason, from the viewpoints of homogenization and dispersion stability of the Ag paste, it is preferable to prevent the Ag powder from drying and always maintain the surface of the Ag powder wet with the solvent. Thereby, a highly conductive electrode can be realized more stably.

[Use of Ag paste]
The Ag paste disclosed herein is characterized in that a sintered body having excellent conductivity can be formed by heating and firing for a short time at a temperature of typically 150 ° C. or lower. Furthermore, aggregation and precipitation of Ag fine particles are highly suppressed, and a stable dispersion state can be maintained over a long period of time.
Therefore, taking advantage of this feature, for example, it can be suitably used in applications in which electrodes and electronic wiring are formed on a substrate made of a material having low heat resistance (for example, a material having a heat resistant temperature of 150 ° C. or lower). A typical use example is formation of a wiring circuit of a touch panel using a resin film such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) as a substrate. Furthermore, if high conductivity can be achieved at a firing temperature of 80 ° C. or less, it can be applied to a material having a lower melting point, for example, a resin film such as polypropylene (PP), paper, and the like. Can spread further. This is also preferable from the viewpoint of reducing the environmental load (for example, energy saving and CO ₂ reduction).

Further, the Ag paste disclosed herein can be preferably used for forming a fine-line electrode (fine line electrode). That is, in the fine line electrode, the resistance increases unless the electrode is thickened (bulky) by the thinning. For this reason, for thinning the electrode, increase the electrode thickness, that is, increase the ratio (H / W) of the electrode thickness H to the line width W. same as below. ) Is required at the same time.
According to the Ag paste disclosed here, a highly dense electrode can be realized, and even if a relatively thick electrode is formed, problems such as cracking and chipping hardly occur in the electrode. Therefore, for example, it can be particularly suitably used in applications for forming fine line electrodes having the following shapes.
Line width W (wide): 100 μm or less (for example, 70 μm or less, preferably 50 μm or less, more preferably 20 μm or less)
Thickness H (height): 10 μm or more (for example, 30 μm or more, preferably 50 μm or more)
-Ratio of thickness H to line width W (H / W ratio): 1 to 0.2

[Method of forming electrode]
In forming the electrode, first, an Ag paste disclosed herein and a desired substrate are prepared. Next, an Ag paste is applied on the substrate so as to have a predetermined line width and thickness. The Ag paste can be applied by, for example, screen printing, slit coater, gravure coater, dip coater, metal mask, dispenser or the like. Thereafter, under a predetermined temperature condition (typically 150 ° C. or lower, preferably 120 ° C. or lower, more preferably 100 ° C. or lower, for example 80 ° C. or lower) for a predetermined time (typically 1 to 60 minutes, for example 10 ~ 30 minutes) Heat drying to burn off the protective agent and dispersion medium and sinter the Ag fine particles. Thereby, a film-like conductor (electrode) can be produced.
In the Ag paste disclosed here, the boiling point of the dispersion medium is kept low at 150 ° C. or lower. Therefore, even after the Ag paste is applied, a uniform electrode can be formed with little variation in film thickness without providing a drying step that is usually required.
As described above, it is preferable from the viewpoint of improving the production efficiency, reducing the cost, and reducing the environmental burden (for example, energy saving and CO ₂ reduction) that the baking can be performed at a low temperature and in a short time and that the drying step can be omitted. .

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

[Synthesis of Ag powder]
Here, first, nine types of Ag powders (a to e, g to j) having different particle size distribution / aspect ratio / protective agent types and amounts were synthesized. Specifically, a solution in which an organic amine described in Table 2 and alcohol (butanol) as a particle size controlling agent were mixed at a predetermined molar ratio in a room temperature environment was prepared. Silver oxalate was added thereto and heated to about 100 ° C. with stirring to obtain an Ag powder having an organic amine attached thereto. Here, the addition amount of the particle size control agent (molar ratio of organic amine and the particle size control agent) was adjusted particle size distribution and D ₅₀ particle size of the Ag powder.

〔Evaluation item〕
The following items (I) to (IV) were evaluated for the obtained Ag powder.
(I) FE-SEM observation The shape of Ag fine particles constituting the Ag powder was observed using a field emission scanning electron microscope (FE-SEM: manufactured by Hitachi High-Technologies Corporation, S-4700). Specifically, first, the obtained Ag powder was dispersed in ethanol as a dispersion medium, and this was applied on an aluminum foil to prepare an observation sample. This sample was observed with an FE-SEM to obtain an observation image. The results (observed images) are shown in FIGS. 1 (a) to (e) and (g) to (j).

(II) Evaluation of particle size distribution From the FE-SEM observation image obtained above, the area equivalent circle diameter was calculated for at least 500 Ag fine particles, and the particle size distribution based on the number was obtained. The results (graphs) for each example are shown in FIGS. 2A (a) to (e) and FIGS. 2B (g) to (j). Table 1 also shows the minimum D _min particle size (nm), D ₅ particle size (nm), D ₁₀ particle size (nm), D ₂₀ particle size (nm), D ₅₀ particle size (nm), D ₈₀ particle size (nm), D ₉₀ particle size (nm), D ₉₅ particle size (nm), maximum D _max particle size (nm), and the spread of the particle size distribution calculated from these particle size values are shown.

(III) Evaluation of aspect ratio The aspect ratio (major axis / minor axis) of at least 500 Ag fine particles was calculated from the obtained FE-SEM observation image. The results (graphs) according to each example are shown in FIGS. 3A (a) to (e) and FIGS. 3B (g) to (j). Further, the ratio (number%) of spherical Ag fine particles having an aspect ratio of less than 1.5, the ratio (number%) of nonspherical Ag fine particles having an aspect ratio of 1.5 or more, and the ratio (number of Ag fine particles having an aspect ratio of less than 2.0). %) And the maximum values are shown in Table 2.

(IV) Quantification of organic amine The organic amine contained in the Ag powder was quantified using a thermogravimetric apparatus. Specifically, the Ag particles were washed with methanol, dried under reduced pressure at room temperature for 20 minutes, and lightly ground in a mortar to obtain a measurement sample. From room temperature to 600 ° C., 10 ° C./min. The rate of weight loss was measured by raising the temperature at a rate of, and the obtained value was taken as the organic amine content. Table 2 shows the organic amine content (mass%) when the Ag powder is 100 mass%.

[Preparation of Ag paste]
Ag pastes (Examples 1 to 8, Reference Examples 1 to 5) were prepared using the obtained Ag powder. Specifically, the Ag powder described in Table 3 was first washed with the dispersion medium described in Table 3, and after centrifugation, the supernatant was discarded. The Ag powder kept in a wet state with the dispersion medium was transferred to a paste container, and the dispersion medium was added so that the content of the Ag powder was 60 to 85% by mass. This was hermetically sealed and placed in a rotating and revolving mixer Awatori Nertaro (registered trademark, manufactured by Shinky Co., Ltd.), and mixed at 1,000 to 2,000 rpm for 1 to 2 minutes. This obtained the Ag paste which concerns on Examples 1-8 and Reference Examples 1-5. In Examples 1 to 4 and Reference Example 5, Ag powder a having the same properties is used and conditions other than Ag powder are examined.

[Sintering test (Evaluation of conductivity)]
The prepared Ag paste was applied onto a PET film as a substrate using a metal mask with a thickness of 100 μm having 1 cm × 1 cm square holes. Immediately after the application, it was put into a blow drying oven set at a predetermined temperature (100 ° C. or 80 ° C.), and taken out after 10 to 30 minutes. FIG. 4 shows photographs of the sintered bodies according to Example 1 and Reference Example 1. 5A and 5B show FE-SEM images after firing under the conditions of 100 ° C./10 minutes according to Example 1 and Reference Example 1. FIG.
And the sheet resistance value and film thickness of the obtained sintered compact were measured. Loresta GP (MCP-T610 manufactured by Mitsubishi Chemical Analytech) was used for the measurement of the sheet resistance value. A thickness measuring device (TH-102 manufactured by Tester Sangyo) was used for measuring the film thickness. The results are shown in Table 3. The volume resistivity shown in Table 3 was calculated as the product of the sheet resistance value and the film thickness.

As shown in Table 3, in Reference Examples 1 and 3, the sintered body was severely cracked, and the resistance value could not be measured. In Reference Examples 1 and 3, all the fine particles exhibited a green color peculiar to the nanoparticles, and almost no color change was observed after firing. In general, when silver forms a sintered body, the green color peculiar to nanoparticles is lost and the color changes to white silver (see Patent Document 1). From this, it can be said that the reference examples 1 and 3 are difficult to sinter in a short time. The reason the content of the protective agent (became 2 mass% or more) which increased to D ₅₀ particle size is small it is conceivable.
Further, in Reference Example 2, a sintered body was formed by firing at 100 ° C./10 minutes, but it was gold instead of white silver, and the volume resistivity was relatively high at 29 μΩ · cm. In Reference Example 4, as in Reference Example 2, the sintered body was gold and the volume resistivity was as high as 472 μΩ · cm.
Further, in Reference Example 5, since hexanol having a high boiling point was used as the dispersion medium, the dispersion medium could not be completely evaporated by short-time low-temperature firing (the dispersion medium remained), and a stable sintered body could not be obtained. .

  In contrast to these reference examples, in Examples 1 to 8, no defects such as cracks were observed in the sintered body, and the volume resistivity was 10 μΩ · cm or less under the firing conditions of 100 ° C./10 minutes, and 80 ° C./10 minutes. An extremely low resistance sintered body having a volume resistivity of 25 μΩ · cm or less under the above firing conditions and a volume resistivity of 10 μΩ · cm or less under the firing conditions of 80 ° C./30 minutes could be realized. That is, it turned out that the Ag paste which concerns on Examples 1-8 shows the outstanding electroconductivity by short-time low-temperature baking.

[Dispensing test with dispenser]
Using an air-type dispenser (AD-2000C manufactured by Iwashita Engineering Co., Ltd.), an Ag paste was continuously discharged at an air thickness of 0.1 to 0.2 MPa from a discharge portion having an inner diameter of 400 μm, and continuous discharge properties were confirmed ( (See FIG. 6). In addition, when an aggregate exists in Ag paste, clogging will arise inside a dispenser and continuous discharge will become impossible.
When the discharge test was performed using the Ag pastes of Examples 1 to 8, all of them were discharged smoothly and continuously for 5 minutes, and a line having a line width of about 300 to 500 μm and a height of 100 to 300 μm could be suitably drawn. It was. From this, it was confirmed that the Ag paste disclosed here does not contain aggregates and dried solidified products and can be used stably.

[Storage stability test]
The Ag pastes of Examples 1 to 8 were stored in a sealed container in a refrigerator at 10 ° C. or lower. After taking out after one month and confirming performance (for example, volume resistivity), it was confirmed that there was no change before and after storage. From this, it was confirmed that the Ag paste disclosed here has high storage stability.

  Although the present invention has been described in detail above, these are merely examples, and the present invention can be variously modified without departing from the gist thereof.

Claims (5)

An Ag paste containing Ag powder and a dispersion medium,
The Ag powder has the following conditions:
(1) In a number- based particle size distribution based on observation with a scanning electron microscope , the D ₅₀ particle size corresponding to a cumulative number of 50% from the smaller particle size is 80 nm or more and 200 nm or less;
(2) The ratio of spherical Ag fine particles having an aspect ratio of less than 1.5 is 60% by number or more and less than 85% by number of the whole Ag fine particles constituting the Ag powder;
(3) A protective agent made of an organic amine having 5 or less carbon atoms is attached to the surface;
(4) When the Ag powder is 100% by mass, the protective agent is 1.2% by mass or less;
(5) In a number-based particle size distribution based on observation with a scanning electron microscope, D ₉₀ particle size corresponding to ₉₀ % by number cumulative from the smaller particle size and D ₁₀ corresponding to ₁₀ % number cumulative from the smaller particle size The particle size and the D ₅₀ particle size satisfy the following formula: 0.7 ≦ [(D ₉₀ particle size−D ₁₀ particle size) / D ₅₀ particle size] ≦ 1.1;
Have both,
The said dispersion medium is Ag paste comprised from the solvent whose boiling point in atmospheric pressure is 150 degrees C or less. The D ₉₀ particle size, and the said D ₁₀ particle size, the next formula: 70 nm ≦ _{(D 90} particle size _{-D 10} particle size) ≦ 210 nm; meet, Ag paste according to claim 1. The _{D 10} particle size is 50nm or more 100nm or less, Ag paste according to claim 1 or 2. The _{D 90} particle size is 120nm or more 310nm or less, Ag paste according to any one of claims 1 3. An Ag powder for use in an Ag paste for electrode formation, under the following conditions:
(1) In a number- based particle size distribution based on observation with a scanning electron microscope , the D ₅₀ particle size corresponding to a cumulative number of 50% from the smaller particle size is 80 nm or more and 200 nm or less;
(2) The ratio of spherical Ag fine particles having an aspect ratio of less than 1.5 is 60% by number or more and less than 85% by number of the whole Ag fine particles constituting the Ag powder;
(3) A protective agent made of an organic amine having 5 or less carbon atoms is attached to the surface;
(4) When the Ag powder is 100% by mass, the protective agent is 1.2% by mass or less;
(5) In a number-based particle size distribution based on observation with a scanning electron microscope, D ₉₀ particle size corresponding to ₉₀ % by number cumulative from the smaller particle size and D ₁₀ corresponding to ₁₀ % number cumulative from the smaller particle size The particle size and the D ₅₀ particle size satisfy the following formula: 0.7 ≦ [(D ₉₀ particle size−D ₁₀ particle size) / D ₅₀ particle size] ≦ 1.1;
Ag powder comprising any of the above.